The building is a little jewel itself.
Built by Cardinal Girolamo Capodiferro around 1548, the facade is decorated with the statues of famous Roman personalities, countered in the inner courtyard by Pagan deities, a tribute to the love for antiquity and the Roman ancestry of the Cardinal.
Later on the building was purchased by Cardinal Bernardino Spada, who turned it into his Roman residence and decorated it further promoting his love for alternative spacial solutions, among which the famous Prospettiva is included.
The First Hall was a series of little rooms that formed the place that hosted the quarters of Girolamo during Winter; on 1653 Bernardino changed this setting, turning the area into a main hall for official meetings.
It's nicknamed "The Hall of Popes" because originally it hosted a series of texts pertaining the lives of Popes, applied on the ceiling. The actual decoration is dated 1777.
In this room you can find a good amount of portraits dedicated to Bernardino and a huge painting of Cardinal Fabrizio Spada, his nephew, who kept increasing the family collection.
The Second Hall was nicknamed "The Flemish Hall", as it was decorated by a precious boiserie designed by Bernini and created by Andrea Battaglini. It was conceived as a study and it wasn't supposed to host paintings but only the current frieze over the ebony panels.
The decoration (tempera on canvas) is the job of Perin del Vaga, and it's actually the project for a tapestry that was supposed to be placed under the frescoes of Michelangelo in the Sistine Chapel.
The Third Hall is definitely the most amusing.
Nicknamed "The Gallery of the Cardinal" it hosted the collection of Bernardino and his brother Virgilio first and Fabrizio then. It was originally a landing; Fabrizio closed the wall and added the windows in place of the original doors, turning it into a closed space.
This hall contains also a good number of paintings dedicated to Cleopatra... The fun note is that she's usually represented as a very Western woman with blonde hair!
The Fourth Hall was made by closing another balcony, turning it into another study; here where preserved the most precious pieces; now it's dedicated to the Caravagesques.
Once back at the entrance, I went through a side door into the tiny courtyard featuring the famous Prospettiva!
Borromini asked for the help of the Augustinian father Giovanni Maria da Bitonto, who took care of the mathematical part of the project.
It was later commented by a short poem of Cardinal Bernardino Spada, too, that gave a moral value to the work, explaining how things that we deem "big" and important in life are actually quite insignificant...